The purpose of a brush in an electrical device is to pass electrical current from a stationary contact to a moving contact surface, or vice versa. Brushes and brush holders are used in electrical devices such as electrical generators and electrical motors of all sizes. They are also used on slip ring assemblies, for example, slip ring assemblies on a rotating machine such as a rotating crane. Brushes in many electrical devices are blocks or other structures made of conductive material, such as graphite, carbon graphite, electrographite, metal graphite, or the like, that are adapted for continuous contact with a conductive surface to pass electrical current. A brush typically includes one or more electrical shunts or wires to provide an electrical current path from the brush to other structure. Typically a brush assembly provides for continuing contact between a stationary brush and a moving conductive surface, or vice versa. Over time, the brush will be reduced in size, or get shorter, for example as the contact surface of the brush wears down. It would be desirable to provide a brush assembly that allows for continuing good contact even as the brush wears down, and which enables quick, safe replacement of brushes.
In many designs, a brush box type brush holder is used to support the brush during operation. The brush and box are designed such that the brush can slide within the box to provide for continuing contact between the brush and the conductive surface contacted by the brush. During wear of a brush, fine particles and/or dust can be created, which can collect on nearby surfaces and the inside of the brush box. Such material can create deposits of brush material on the inside of the brush box that can restrict sliding movement of the brush within the box, which in turn can reduce the quality of the contact between the brush and the contact surface. It would be desirable to provide a brush assembly that allows for a reduction of such restriction in movement of the brush. Additionally, it would be desirable to provide a brush assembly which does not allow current to pass through the box to thereby avoid detrimental effects, such as electrical erosion of the surfaces of the box, or collection of deposits on the surface of the box, which can restrict movement of the brush within the box.
Further, typically such boxes include a back plate which is used to enable a spring to press the brush against a conductive surface. It would also be desirable to provide a brush assembly which can function without requiring a back plate.
In some instances a brush may become so worn as to require replacement. In some such cases, for example in power generation, it may be difficult or expensive to stop the motion of the moving conductive surface to replace the brush. However, removal of the brush while relative motion between the brush and the conductive surface is ongoing can create a risk of arcing between the brush and the conductive surface, or can create a risk of accidental short circuiting the flow of electricity in other components. It would be desirable to provide a brush assembly that allows for safe, easy removal and replacement of a worn brush without requiring an adjacent collector ring, commutator or other moving part to be stopped.